The asymptomatics riddle: Role in Covid-19 spread unclear; enforce mask-use, distancing

The fight against Covid-19 will have to deal with the questions surrounding asymptomatic infected cases: how many will likely not experience any symptoms, how big is their role in the spread of the disease, is the chance of being asymptomatic higher for a particular demography (age-wise/sex-wise), etc. These questions are further complicated by the unclear line between true asymptomatics (those who course through the disease without ever having exhibited symptoms) and the pre-symptomatics (those who are infected but have no symptoms at the time of the infection getting reported, only to develop these later).

The lack of a standard definition for pre-symptomatics—in terms of a threshold duration before the onset of symptoms, or some such yardstick—plays its part too.

Early in the pandemic, there had been talks of a high asymptomatic proportion in the pool of infected—the ICMR pegged this at 70% cases though it later tempered that estimate drastically. However, last month, an analysis of 13 low-risk-of-bias studies from seven countries, with data on 21,708 high-risk people, showed asymptomatic people constitute merely 17% of the infected population.

The meta-study also found that asymptomatics were 42% less likely to spread the disease than those with symptoms. Another study, uploaded on the pre-print server, medRxiv, found that the risk of an asymptomatic case passing on the disease to others in their home was a fourth that of a symptomatic case doing this.

The new research seems to be at odds with the disease data in the Indian context, specifically the large gap between reported cases—based on largely symptomatic-focused testing—and serosurvey findings; the number of reported infections on the last day of the latest countrywide serosurvey (September 22) stood at 56 lakh versus the 9.1 crore estimated from the serosurvey findings. It is quite unlikely that there were so many symptomatic cases that never got tested/reported.

Read with the fact that the estimate of infected jumped from around 1 crore in the first serosurvey to 9.1 crore in the second (three months after the first)—and that the bulk of the symptomatic cases would have taken some isolation measures—this would suggest a much larger role of asymptomatics.

There are very few things that we can hold as canonical when it comes to Covid-19; while the scientific opinion is that asymptomatics neutralise the virus faster than symptomatics, there have been cases where an asymptomatic individual has remained infectious for a long time—in one case, as long as 70 days.

So, whether the number of asymptomatics is low or high, whether they transmit the virus at a comparable rate with symptomatics or not, pending pharmacological solutions, the policy must double down on non-pharmacological measures—to that end, the Delhi government’s move to increase the ‘no-mask’ fine from Rs 500 to Rs 2,000 is a good move.